Assembly for an air separator and method for controlling the function of the same

ABSTRACT

An assembly is disclosed for an apparatus used for deaeration of treatment agents applied to webs of paper and board, the assembly comprising at least one inlet manifold ( 3 ), at least one accept-fraction manifold ( 4 ), and at least one reject-fraction manifold ( 5 ) with associated framework structures; also a method is disclosed for operating the assembly. For deaeration the assembly uses a plurality of air separator units ( 12 ) connected to the manifolds so as to allow admission of the treatment agent to the air separator units ( 12 ) from the inlet manifold ( 3 ) and discharge of the accept and reject fractions formed in the air separator units ( 12 ) respectively to the accept-fraction and reject-fraction manifolds ( 4, 5 ). A cut-off valve ( 18 ) is mounted on at least the inlet manifold ( 3 ), between two parallel-operating air separator units ( 12 ), so as to permit cutting off the flow through the manifold ( 3 ) at this location of the cut-off valve thus dividing the plural air separator units ( 12 ) by the cut-off valve ( 18 ) into two groups.

[0001] The present invention relates to an assembly according to thepreamble of claim 1 for use in an apparatus serving for deaeration oftreatment agents applied to webs of paper and board, whereby theassembly makes it possible to adjust the capacity of the air separatorfor different volumetric flow rates.

[0002] The invention also relates to a method for controlling theoperation of an air separator.

[0003] In coating a web of paper or board, a treatment agent such aswater-based size or pigment mixture is applied to the surface of the webto be treated. Conventionally, the treatment agent is applied in anexcess amount and the surface of the treated web is smoothed by means ofa doctor. The excess amount is returned after straining back to the maincirculation of the treatment agent stock. Additionally, applicators of atreatment agent frequently use a flushing circulation or the like,wherefrom also a certain amount of the treatment agent is returned afterstraining back to the main circulation. Particularly during applicationand doctoring, air may have access into the treatment agent stock,whereupon the entrained air and bubbles may cause profile defects andeven uncoated spots on the layer of applied treatment agent. Entrainedair causes the greatest problems in coating with a pigment-containingcoating mix and particularly problematic are such processes that involvehigh shear rates of the coating mix. The problem appears moreaccentuated with certain types of coating formulations that are prone toentrain large volume of air. Such formulations are talc-containingcoating mixes, for instance. Accordingly, it is imperative to separateair as efficiently as possible from the web treatment agent before itspumping to the applicator apparatus.

[0004] In U.S. Pat. No. 4,170,457 is disclosed one kind of air separatorcomprising a cylindrical tank rotatable about a vertical axis. Thecoating liquid stock is pumped into the tank via its top and, under theeffect of the centrifugal action, the coating liquid is driven onto thetank walls, whereby the air-laden portion of the coating stock remainsin the radially central region of the tank and may thus be removedtherefrom via the top of the tank. This apparatus is relativelycomplicated and needs a drive motor. As the apparatus contains movingparts, it needs scheduled maintenance and replacement of worncomponents. U.S. Pat. No. 4,390,351 describes an apparatus comprised ofa spiraling tube or the like passage through which the liquid is forcedto pass. The channel has specific compartments and spaces formedthereto, wherein the entrained air bubbles can be separated from theliquid circulating in the spiraling passage. While this apparatusfeatures a simple construction, its efficiency is rather poor.

[0005] In FI Pat. No. 98,792 is disclosed a relatively efficient airseparator apparatus. In this embodiment, the liquid or other mixtureflowing therethrough is admitted tangentially into the upper region of acylindrical separator tube, wherein the liquid is forced into a rapidvorticous motion. Herein, the air-laden fraction of the liquid is forcedinto the radially central region of the cylindrical separator tube andcan be removed centrally from the tube at the lower end thereof. Theair-free fraction is similarly removed from the lower end of the tube,at the radially marginal region of the tube. To attain a good airseparation efficiency in this kind of apparatus, a relatively highvelocity is required from the inlet flow. For this purpose, thediametral dimensions of the cylindrical separator tube and itsinlet/outlet nozzles need to be made sufficiently small to ensure such arapid flow velocity at the available flow rate. Another vital reason forthe use of a small-diameter cylindrical separator tube is that hereby ashort transit distance of entrained air bubbles from the peripheralregion of the tube to the center of the tube becomes short, whereby afaster and thus more efficient separation is attained. Hence, this kindof air separator is generally operated in parallel groups so that thecombined capacity of all the air separators in the group is sufficientfor handling the required volumetric flow rate. The air separators aregrouped so that, e.g., their inlet nozzles are connected to an inletmanifold and the reject/accept fraction outlet nozzles are respectivelyconnected to a reject discharge manifold and an accept outlet manifold.In this fashion, the air separator assembly can be readily dimensionedfor a desired capacity while simultaneously assuring a sufficiently highflow velocity in the separator units that is needed for efficient airseparation. An air separator assembly formed according to these designrules may comprise, e.g., 5 to 30 separator units connected to commonmanifolds.

[0006] The individual separator units can be isolated from the manifoldsby manual cut-off valves or plugs. During a normal production run, theoutput flow rate of the pump that circulates the treatment agent in themachine circulation of an applicator apparatus is substantially constantwithin a minor deviation range depending on the running speed of theapplicator section of the coating mix or size. By setting the capacityof the air separator assembly through shutting off a suitable number ofthe separator units by plugging or operation of the manual cut-offvalves so as to comply with the actual output of the machine circulationpump during the run, it is generally possible to match the capacity ofthe air separator assembly fairly well with the requirements of theapplicator apparatus over its normal range of web speeds. Hence, thereis no need during a normal production run for adjusting the airseparator capacity.

[0007] During production shut-down periods and otherwise when no coat orsize application is performed, the pump output is decreased to a lowlevel of about 20% known as the stand-by circulation rate. It isdisadvantageous to cut off the circulation entirely, because restartingthe machine circulation of the treatment agent subsequently interfereswith the run-up of the entire production line, and additionally incursthe risk of plugged circulation by dried clumps of the treatment agent.With the decreased overall circulation rate, also the flow rate througheach separator unit falls even down to a level so low as to compromiseefficient air separation in any one of the separator units. Resultingly,the stand-by flow rate produced by the circulation pump allows admissionof air into the machine circulation of the treatment agent. During therestart of application and the run-up of the circulation pump output tothat required for application, it takes several minutes to reduce theentrained air content of the treatment agent down to the low levelcorresponding to the normal application run state. During this transientperiod of time, the paper qualities such as its coat evenness, forinstance, fall short of preset specifications thus requiring dumping ofthe produced web into the broke pulper. In fast-running applicators thiscauses a substantial production loss and, obviously, a longer productionshut-down.

[0008] The above-described problem can be avoided by way of replacingthe manual valves of the inlet, accept and reject fraction manifolds byautomatic valves, whereby a desired number of separator units can beshut off from the circulation in the stand-by state. As such a shut-offoperation must be carried out rapidly, manual valves are clumsy tomanipulate when the separator assembly is to be adjusted to the stand-bystate and, vice versa, it is practically impossible to open a largenumber of manual valves at the run-up of the circulation pump for thehigher output. Herein, it must be appreciated that as each separatorunit is equipped with three manual valves and the assembly may compriseup to 30 separator units, at the instant of circulation pump outputincrease for full-speed operation an enormous task emerges to open allthe valves momentarily. As to the use of automatically controlledvalves, this is a disadvantageous alternative inasmuch a large number ofautomatically controlled valves incurs a higher cost and the fitting ofautomatic valves with actuators into the limited space between thenozzles and the manifolds requires a greater space between the separatorunits and outdistancing of the same from the framework of the airseparator assembly, whereby inevitably also the external dimensions ofthe air separator assembly become larger. This is awkward and, hence,retrofitting an air separator to the treatment agent machine circulationof older applicator sections in particular is frequently complicated bythe insufficient footprint of available installation space. Accordingly,it is desirable to achieve a method and assembly that could permit theadaptation of an air separator in a simple manner to the requirements ofa reduced volumetric flow rate of circulating treatment agent.

[0009] It is an object of the present invention to provide an assemblyoffering flow-rate-based capacity adjustment in equipment serving forair separation from treatment agent mixtures used in application to aweb of paper or board.

[0010] The goal of the invention is achieved by virtue of equipping atleast the inlet manifold or accept manifold of an air separator with avalve, advantageously an automatically controlled valve, that cuts offflow in the manifold so as to permit passage of the treatment agent flowfrom the manifold only to certain ones of the air separator units of theassembly.

[0011] According to a preferred embodiment of the invention, theautomatically controlled valves are fitted not only to the inletmanifold, but also at respective points of the accept and rejectmanifolds.

[0012] More specifically, the assembly according to the invention ischaracterized by what is stated in the characterizing part of claim 1.

[0013] Furthermore, the method according to the invention ischaracterized by what is stated in the characterizing part of claim 4.

[0014] The invention offers significant benefits.

[0015] The invention makes it readily possible to adapt an air separatorfor two different separation capacities. The modifications required onan existing air separator are minimal and the overall cost of the airseparator is increased only slightly. The modification is mechanicallyand structurally simple to carry out and, moreover, the externaldimensions of the air separator can be retained almost unchanged ascompared to those of an unmodified separator. Resultingly, the airseparator improved according to the invention can be fitted in a smallspace, which is an advantage in revamping the treatment agent machinecirculation of older applicator sections.

[0016] In the following, the invention will be examined in more detailby making reference to the appended drawings in which

[0017]FIG. 1 is a side view of an embodiment according to the invention;and

[0018]FIG. 2 is an end view of the apparatus of FIG. 1.

[0019] The present invention is directed to an air separator thatadvantageously is based on air separator units 12 according to FI Pat.No. 98,792. The function of these air separator units 12 is described inmore detail in cited patent publication, which is appended to thisapplication by way of reference. In this type of air separator 12, thetreatment agent is admitted to the separator 12 via its infeed nozzleinto the upper region of the separator, wherein the treatment agent isbrought into a vorticous motion in the interior of the elongatedcylindrical vessel of the separator 12 and the air-laden fraction of thetreatment agent thus seeks to the radially central region of thecylindrical vessel while the deaerated treatment agent itself is drivento the radially outer region of the cylindrical vessel. The air-freeaccept fraction of the treatment agent is removed from the lower portionof the cylindrical vessel at the inner perimeter thereof and theair-laden reject fraction is discharged via the bottom end of thecylindrical vessel, at the central axis thereof.

[0020] In an air separator assembly, air separator units 12 areconnected to the framework of the assembly by a number of unitssufficient to provide the required separation capacity. The framework ofthe air separator assembly comprises an inlet manifold 3, an acceptfraction manifold 4 and a reject fraction manifold 5. The manifolds 3,4, 5 are terminated at end flanges 1 and 2. The inlet-side flange 2 hasopenings made thereto for the flow passing in the manifolds 3, 4, 5,while the outlet-side end flange 1 has blind flanges 15, 16, 17 mountedthereon for closing the ends of the manifolds. The reject-fractiondischarge manifold 5 is connected via blind flange 17 by means offlexible hoses 9, 10 equipped with manual valves to blind flange 16 ofthe accept-fraction manifold 4 and blind flange 15 of the inlet manifold3. Hoses 9, 10 make it possible to interconnect the manifolds forflushing or washing the ends of the manifolds.

[0021] As shown in FIGS. 1 and 2, the air separator assembly comprises16 pcs. air separator units 12 mounted on both sides of the manifolds 3,4, 5. The inlet nozzles of the air separator units 12 are connected tothe inlet manifold via manual valves 6 and the accept-fraction outletnozzles are connected to the accept-fraction manifold 4 via manualvalves 7. Respectively, reject discharge nozzles are connected to thereject-fraction manifold 5 via a hose 8 equipped with a manual valve 11.Thus, the manual valves 6, 7, 11 make it possible to disconnect as manyindividual air separator units off from the circulation as are requiredto match the capacity of the air separator assembly to the run-timevolumetric flow rate of the machine circulation of the applicatorapparatus.

[0022] When the air separator described above is in its run-timeproduction use, the treatment agent is admitted in the air separatorfirst into the inlet manifold 3, wherefrom its passes via the airseparator units 12 so as to separate therein into accept and rejectfractions that are further passed to their respective manifolds andtherefrom out of the air separator assembly. For reduced capacity duringstand-by circulation periods, the air separator assembly has cut-offvalves 18, 19 and 20 mounted on the manifolds 3, 4, 5. These cut-offvalves in the illustrated embodiment are located after the two first airseparator units 12 as counted from the inlet-side main flange 2, wherebya total number of four air separator units 12 remain between the cut-offvalves 18, 19, 20 and the inlet-side main flange 2. Respectively, atotal number of 12 air separator units remain on the opposite side fromthe cut-off valves. This division ratio gives a reduced capacity thatgenerally matches with the 20% stand-by output of the machinecirculation pump as compared to its run-time output during fullproduction. obviously, the position of the cut-off valves on themanifold is selected so that the thus achieved reduction of separatorcapacity matches with the capacity need ratio between the run-time andstand-by states of the treatment agent machine circulation.

[0023] The embodiment according to the invention is simply operated sothat when the machine circulation pump is controlled to its stand-byoutput, the cut-off valves are automatically closed by a suitablecontrol command that may be linked to, e.g., the pump output control,the control computer of the air separator assembly or a command issuedfrom the operator console. Respectively, the cut-off valves are openedwhen the run-time separator capacity of full production is assumed. Anessential requirement herein is that the closing/opening of the valvesmust take place sufficiently accurately synchronized with the control ofthe machine circulation flow rate so that the flow in the air separatorunits will not slow down nor there will occur any detrimental pressureshocks or elevations. The valves can be of any suitable type and theircontrol may be implemented using conventional actuators capable ofoperating the valves, e.g., by electrical, hydraulic or pneumatic means.

[0024] In addition to those described above, the invention may havealternative embodiments.

[0025] In principle, a cut-off valve is needed only on the inletmanifold or the accept-fraction manifold, because either one is capableof blocking the circulation of the treatment agent in separator unitsthat are located downstream from the cut-off valves. However, if thereject-fraction and accept-fraction manifold are not respectively cutoff, there may occur some degree of disturbing sideflows and backflowsin the assembly as well as a partial emptying of the manifolds, wherebythe drying of treatment agent becomes an imminent risk. In contrast, afull cut-off of all manifolds assures unchanged moisture content in theclosed section of the air separator assembly and at least the rate ofdrying is slowed down. For these reasons, it is a good practice to mountcut-off valves at least on the inlet and accept-fraction manifolds, evenmore advantageously on all manifolds in accordance with theabove-described embodiment.

[0026] The invention may generally be applied to all such air separatorinstallations that use a plurality of air separator units. However, theabove-described type of air separator has proven its merits by itssimplicity and efficiency. The number of the air separator units and theposition of the cut-off valves may be varied and, when necessary,cut-off valves can be fitted only on one side of the manifolds. Inprinciple, the assembly could be implemented using a plurality ofparallel manifolds, but in the interest of a more efficient utilizationof the overall footprint, it may be preferable to install a plurality ofparallel-operating air separator assemblies if necessary to attain aspecified capacity. In the context of this application, the termmanifold must be understood broadly to refer to any chamber-like space,not only to a straight tubular manifold. However, the division of flowsin other shapes of manifold chambers by means of valves is clumsier andmay possibly require the use of large gate valves, for instance.

What is claimed is:
 1. Assembly in an apparatus used for deaeration oftreatment agents applied to webs of paper and board, the assemblycomprising at least one inlet manifold (3), at least one accept-fractionmanifold (4), at least one reject-fraction manifold (5), a framework (1,2) having the manifolds (3, 4, 5) fixed thereto, and at least two airseparator units (12) connected to the manifolds so as to allow admissionof the treatment agent to the air separator units (12) from the inletmanifold (3) and discharge of the accept and reject fractions formed inthe air separator units (12) respectively to the accept-fraction andreject-fraction manifolds (4, 5), characterized by at least one cut-offvalve (18) mounted on at least either one of said accept-fraction andinlet manifolds, between two parallel-operating air separator units(12), so as to permit cutting off the flow through said manifold (3, 5)at said location of said cut-off valve thus dividing said plural airseparator units (12) by said cut-off valve (18) into two groups. 2.Assembly according to claim 1, characterized by cut-off valves (19, 20)mounted on the inlet manifold (3), the reject-fraction manifold (5) andthe accept-fraction manifold (4) and in a similar position as the valvesmounted on the accept-fraction manifold (4) or the inlet manifold (3).3. Assembly according to claim 1, characterized in that said airseparator units (12) are shaped into an elongated cylindrical vesselhaving at its first end equipped with means for admitting the treatmentagent tangentially into the cylindrical vessel and at its other endmeans for discharging the reject-fraction from the radially centralregion of the cylindrical vessel and for removing the accept-fractionfrom the radially marginal region of the cylindrical vessel.
 4. Methodfor deaeration of treatment agents applied to webs of paper and board,the method comprising the steps of admitting the flow of the treatmentagent via an inlet manifold (3) into at least two air separator units(12), separating the flow of the treatment agent in the separator units(12) into an accept fraction and a reject fraction, and discharging saidfractions from said air separator units (12) characterized in that theflow is cut off in at least either one of said accept-fraction and inletmanifolds (3, 4), between two parallel-operating air separator units(12) connected thereto, at the instant a reduced air separation capacityis required.
 5. Method according to claim 4, characterized in that thetreatment agent fractions are separated in said air separator units (12)by means of bringing the treatment agent into a vorticous motion in theinterior of the cylindrical vessel.